58 H. I. JENSEN. 
This rock is certainly later than the Silurian schists and 
probably later than the Devonian, and may even be as late 
as Tertiary, but its exact relations to the Devonian I 
have not yet worked out. The surrounding rocks are 
Devonian shales, quartzites and tuffis. They contain well 
preserved fossils, Rhynconella pleurodon, Spirifer dis juneta 
and Chonetes. The mineralisation of the area appears to 
have taken place in the late Devonian period. 
The Quartz Veins of the Nelligen district share in 
common with most of the auriferous reefs of the Shoal- 
haven district the peculiar property of cutting out ata 
depth of 50-60 feet. This disagreable feature has caused 
the failure of so many mining enterprises on the South 
Coast. 
On my trip through the Nelligen district I noticed in 
many clifi faces and road cuttings many small lenticular 
quartz veins. They commence as a fine streak, gradually 
thicken and thin out again to a streak. Such veins occur 
of all sizes in the Silurian, and are often rich in gold. 
An examination of these veins led me to the view that 
they were formed during the orogenic movements which 
folded, contorted and metamorphosed the Silurian strata. 
In my opinion the heat and pressure due to the orogenic 
disturbances not only crushed, crumbled and recrystallised 
the Silurian sediments, but their original moisture contents 
became vaporised, and performed a pneumatolytic action 
whereby they caused the silica, in excess of what was 
necessary for the formation of metamorphic minerals, to 
tend to separate out in streaks or schlieren in the semi- 
plastic mass. At thesame time gold was leached by these 
vapours out of the sediments and concentrated in the quartz 
veins. 
It is generally supposed that all these quartz reefs, which 
cut out in depth and have no relation to any fissure vein, 
